Freeze Drying | College of Aeronautics and Engineering | Kent State University

The Freeze Drying project is led by Research Team Member Theo Woodson.

photo Theo Woodson headshotThe goal of freeze drying is to perfect a porous tube that will allow hydrogen gas to easily diffuse into a fuel cell, increasing its efficiency. There are many steps to Freeze drying including: Preparation, Freezing, Primary Drying, and Secondary Drying.

The Preparation phase includes mixing the ceramic material that will go into a fuel cell. This mixture is called Slurry, or Slip, and involves many chemical compounds. After the slurry has been created, it will be injected into a mold to create a green tube (which will later become part of the fuel cell).

After the Slurry is prepared, the mold is coated with a single layer of ice. This ice separates the metal of the mold from the tubing that is being created. After the ice layer, a layer of slurry is inserted into the mold.

During the Freezing phase, sublimation occurs. Sublimation is when water transforms from ice to gas, while skipping the liquid phase. Through sublimation, we are able to remove the ice crystals from the slurry, leaving behind in their place empty space. These empty spaces are what cause the material to have a porous structure for gas diffusion.

In the Primary Drying phase, enough heat is applied for the ice to sublime. In this phase, pressure is controlled by a vacuum, which speeds up sublimation.

The Secondary Drying phase is where much of the slurry material experiences shrinkage.

photo Fuel Cell Research freeze drying operation

photo Fuel Cell Research, freeze drying graph